The present invention relates to a method for fabricating a semiconductor device; and, more particularly, to a method for forming a quantum dot.
In accordance with a current scale-down trend due to advanced levels of integration in a semiconductor device, the total number of electrons existing in channel regions will be also decreased by a few tens of electrons.
As the number of electrons necessary for driving the semiconductor device decreases, a percentage of electrons corresponding to a statistic error among those electrons for driving the semiconductor device conversely increase. This increased percentage of the electrons has a severe impact on reliability of the semiconductor device. Therefore, it is evidently required to develop a new structure of the semiconductor device capable of accurately controlling a single electron.
A single electron transistor, recently proposed for coping with the above limitation, is able to control a single electron and drive the semiconductor device even with an extremely low voltage.
In other words, when each of a typical metal-oxide silicon field effect transistor (MOSFET) and the single electron transistor performs the same algorithm, the MOSFET needs about 1000 to about 20000 electrons. However, the single electron transistor needs only about 1 to about several electrons, thereby decreasing power consumption by 1/1000 and further resulting in power-saving and high integration effects.
FIG. 1 is a cross-sectional view showing a single electron transistor in accordance with a prior art.
Referring to FIG. 1, a first insulating layer 12A and a second insulating layer 12B are sequentially deposited on a semiconductor substrate constructed with silicon or Gexe2x80x94AS. A number of quantum dots are formed on between the first insulating layer 12A and the second insulating layer 12B. Herein, the first insulating layer 12A is a tunneling oxide,. and the second insulating layer 12B is a control oxide.
Subsequently, a gate electrode 14 is formed on the second insulating layer 12B. On both ends of the gate electrode 14, a source area 15 and a drain area 16 are formed within the semiconductor substrate 11.
To construct the single electron transistor, it is very important to form uniformly micronized quantum dots of which size is several nanometers on the first insulating layer 12A corresponding to the gate electrode 14.
There suggested several conventional methods for forming quantum dots. A quantum dot can be formed by using the agglomeration phenomenon achieved from serial steps as following: depositing silicon germanium or a thin metal layer on between oxide layers; growing the oxide layers; and treating the grown oxide layers with a thermal process. Lithography can also be used for directly forming a number of quantum dots, or there is another method for forming quantum dots electrically within a gap between energy bands. Yet, there has not been suggested a method for forming a quantum dot satisfying reliability and massproduction simultaneously.
Also, it is limited to improve properties of the semiconductor device since a quantum dot formed through the conventional method forms mainly multi-crystal silicon.
It is, therefore, an object of the present invention to provide a method for forming a quantum dot that has a single crystal and satisfy reliability and massproduction simultaneously.
In accordance with an aspect of the present invention, there is provided a method for forming a quantum dot, including the steps of: forming a first insulating layer on a semiconductor substrate; forming an opening that exposes the semiconductor substrate by etching the first insulating layer; forming a single crystal semiconductor layer in the opening and on the first insulating layer adjacent to the opening; and forming a quantum dot on the first insulating layer adjacent to the opening by removing the single crystal semiconductor layer in the opening and portions of the singly crystal layer on the first insulating layer adjacent to the opening.
In accordance with another aspect of the present invention, there is also provided a method for forming a quantum dot, comprising the steps of: forming a sub-layer on a substrate; forming an opening that expose the substrate by etching the sub-layer; forming a conductive layer in the opening and on the sub-layer adjacent to the opening; and forming a quantum dot by leaving portions of the conductive layer on the sub-layer adjacent to the opening.